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To study a marine organism, a biologist prepares a 1.00-kgsample to simulate the ion concentrations in seawater. She mixes 26.5 g of NaCl, 2.40 g of MgCl₂, 3.35 g of MgSO₄, 1.20 g of CaCl₂, 1.05 g of KCl, 0.315 g of NaHCO₃, and 0.098 g of NaBr in distilled water. (a) If the density of the solution is 1.025 g/cm³,what is the molarity of each ion? (b) What is the total molarity of alkali metal ions? (c) What is the total molarity of alkaline earthmetal ions? (d) What is the total molarity of anions?

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The molarity of each ion is obtained from the number of moles and volume of solution

From the question, the mass of the solution is 1.00 Kg and the density of the sample is 1.025 g/cm³.

From this, we can calculate the volume of the solution as follows;

D = M/V

V = M/D = 1 × 10^3 g/1.025 g/cm³

V = 976 cm³ or 0.976 L

Recall that number of moles = mass/molar mass

For NaCl = 26.5 g/58.5 g/mol = 0.45 moles

For  MgCl₂ = 2.40 g/95 g/mol = 0.025 moles

For MgSO₄ = 3.35 g/120 g/mol = 0.028 moles

For CaCl₂ = 1.20 g/111 g/mol = 0.011 moles

For KCl = 1.05 g/75 g/mol = 0.014 moles

For NaHCO₃ = 0.315 g/84 g/mol = 0.0038 moles

For NaBr = 0.098 g/103 g/mol = 0.00095 moles

Molarity of each solution = number of moles/volume

For NaCl = 0.45 moles/0.976 L = 0.46 M

For MgCl₂ = 0.025 moles/0.976 L = 0.026 M

For MgSO₄ = 0.028 moles/0.976 L = 0.029 M

For CaCl₂ = 0.011 moles/0.976 L = 0.011 M

For KCl =  0.014 moles/0.976 L = 0.014 M

For NaHCO₃ = 0.0038 moles/0.976 L =0.0039 M

For NaBr = 0.00095 moles/0.976 L = 0.00097 M

The molarity of Na^+ and Cl^- = 0.46 M each

The molarity of Mg^2+ = 0.013 M while the concentration of Cl^- = 0.026 M

The molarity of both Mg^2+ and SO4^2- ions are 0.029 M each

The molarity of Ca^+ is 0.0055 M while the concentration of Cl^- is 0.011 M

The molarity K^+ and Cl^- are both 0.014 M

The molarity of both Na^+ and HCO3^- are both 0.0039 M

The molarity of both Na^+ and Br^- are both 0.00097 M

The total molarity of Na^+ = 0.46 M + 0.0039 M + 0.00097 M = 0.465 M

The total molarity of Ca^+ =  0.0055 M

The total molarity of Mg = 0.013 M + 0.029 M = 0.042 M

The total molarity of K^+ = 0.014 M

The total molarity of Cl^- =  0.46 M + 0.026 M + 0.011 M + 0.014 M = 0.511 M

The total molarity of SO4^- = 0.029 M

The total molarity of HCO3^- = 0.0039 M

The total molarity of Br^- = 0.00097 M

The total molarity of alkali metal ions = 0.465 M + 0.014 M  = 0.479 M

The total molarity of alkaline earth metal ions = 0.0055 M + 0.042 M = 0.0475 M

The total molarity of anions = 0.511 M + 0.029 M + 0.0039 M + 0.00097 M = 0.545 M

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